JPH0779452B2 - Liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device used in, for example, a viewfinder of a television camera.

Background Art and Its Problems It has been proposed to display a television image using a liquid crystal.

In FIG. 1, (1) is an input terminal to which a video signal of a television is supplied, and a signal from this input terminal (1) is a switching element M ₁ , which is, for example, an N-channel FET,
M ₂ ... Lines L ₁ and L _{2 in the} vertical (Y-axis) direction through Mm
..Supplied to Lm Note that m is a number corresponding to the number of pixels in the horizontal (X axis) direction. Further, an m-stage shift register (2) is provided, and clock signals Φ _1H and Φ _2H of m times the horizontal frequency are supplied to the shift register (2), and clocks from respective output terminals of the shift register (2). Drive pulse signals Φ _1H , which are sequentially scanned by the signals Φ _1H , Φ _2H
Φ _2H ... Φ _Hm is supplied to each control terminal of the switching elements M _{1 to} Mm. The shift register (2) is supplied with a low potential (V _SS ) and a high potential (V _DD ) and drive pulses of these two potentials are formed.

Further, for example, N-channel FETs are provided on the respective lines L _{1 to} Lm.
Of switching elements M ₁₁ arranged in a matrix,
M ₂₁・ ・ ・ M _n1,, M ₁₂ , M ₂₂・ ・ ・ M _n2 , ・ ・ ・ M _1m , M _2m・ ・ ・ M
One end of the element forming each column line of _nm is connected. Note that n
Is a number corresponding to the number of horizontal scanning lines. The other ends of the switching elements M _{11 to} M _nm are respectively connected to liquid crystal cells C ₁₁ , C ₂₁ ... C.
Connected to the target terminal (3) through _nm .

Further, an n-stage shift register (4) is provided, and a horizontal frequency clock signal Φ _1V ,
[Phi _2V is supplied, the clock signal [Phi _1V from the output terminal of the shift register (4), the driving pulse signal phi _V1 sequentially scanned by Φ _2V, φ _V2 ··· φ _Vn is the switching element M ₁₁ ~ Each line of M _{nm in} the X-axis direction (M _{11 to} M _1m ), (M
_{21 to} M _2m ) ... (M _{n1 to} M _nm ) are supplied to the respective control terminals. Note that V _SS and V _DD are supplied to the shift register (4) as well as the shift register (2).

That is, in this circuit, the shift register (2),
In (4), clock signals Φ _1H , Φ as shown in FIGS.
_2H , Φ _1V and Φ _2V are supplied. Then, from the shift register (2), as shown in FIG.
_{H1 to} φ _Hm are output, and the second from the shift register (4)
As shown in FIG. D, φ _V1 to φ _Vn are output every horizontal period. Furthermore, a signal as shown in FIG. 2E is supplied to the input terminal (1).

When φ _V1 and φ _H1 are output, the switching elements M ₁ and M _{11 to} M _1m are turned on, and the input terminal (1) → M ₁ →
A current path of L ₁ → M ₁₁ → C ₁₁ → target terminal (3) is formed, and the potential difference between the signal supplied to the input terminal (1) and the target terminal (3) is supplied to the liquid crystal cell C ₁₁ . Therefore, the charge corresponding to the potential difference due to the signal of the first pixel is sampled and _{held in} the capacity of the cell C ₁₁ . The light transmittance of the liquid crystal is changed according to this charge amount. The same operation is sequentially performed on the cells C _{12 to} C _nm , and at the time when the signal of the next field is supplied, each cell C _{11 to} C _nm is further supplied.
The charge amount of _nm is rewritten.

In this way, the liquid crystal cell corresponding to each pixel of the video signal
The light transmittance of C _{11 to} C _nm is changed, and this is repeated sequentially to display a television image.

By the way, when displaying with a liquid crystal, an AC drive is generally used in order to improve its reliability and life. For example, in displaying a television image, the video signal is inverted every vertical period and a signal obtained by adding a required DC potential is supplied to the input terminal (1). That is, the input terminal (1) has a second
As shown in FIG. E, a signal that has been inverted and added with a DC potential every vertical period is supplied.

The video signal shown in FIG. 2E is generally formed by the circuit shown in FIG. In the figure, transistors Q ₁ and Q ₂
And Q ₃ and Q ₄ are provided in two sets, and the video signals S _{V of} opposite phase are supplied to the bases of the transistors Q ₁ and Q _{4 and} the bases of Q ₂ and Q ₃ , respectively. Also transistor
Transistors Q ₅ and Q ₆ are provided in the collector current paths of Q ₁ and Q ₂ and Q ₃ and Q ₄ , respectively, and the field pulses Pf of opposite phase are supplied to the bases of the transistors Q ₅ and Q ₆ , respectively. The emitters of the transistors Q ₁ , Q ₃ and Q ₂ , Q ₄ are connected to each other, and the output is taken out from the connection point of the Q ₂ , Q ₄ emitters via the load resistor.

However, in this circuit, the waveform of the output signal is shown in FIG.
, And the emitter-collector voltage of transistor Q ₄ varies from field to field. Therefore transistor Q ₄
The collector current flowing through is modulated by the Early effect, and an output waveform symmetrical to the input cannot be obtained. This corresponds to the fact that the effective voltage applied in each of the liquid crystal cells C _{11 to} C _nm varies from field to field, causing flicker in the image.

Also, because this circuit is composed of double balance type,
The circuit was relatively complicated.

Further, as such a liquid crystal display device, the following devices have been conventionally proposed.

In FIG. 4, the output of the shift register (4) is connected to the control terminals of the switching element elements M _{11 to} M _nm for each column in the X-axis direction through the switching elements M _V1 , M _V2 ... M _Vn , respectively. At the same time, this connection point is connected to the power supply terminal V _SS through the switching elements M _V ′ ₁ , M _V ′ ₂ ... M ₁₇ , respectively. And the switching elements M _{V1 to} M _Vn and M _V ′ ₁
Pulses Pf that are inverted for each field are supplied to the control terminals of M ₁₇ through M ₁₇ in opposite phases. Others are the same as in FIG.

In this device, one frame (2
A video signal S _{V that} is inverted every field is supplied.
The signals of the respective parts are as shown in FIG. When the field pulse Pf supplied to the switching elements M _{V1 to} M _Vn is at a high potential and φ _Hj and φ _Vi are output, the liquid crystal cell Cji
The video signal is sampled and held. This signal is held for two field periods, and the video signal of a new frame is input while the next field pulse Pf is at a high potential.

In this device, the equivalent circuit of the circuit which constitutes one pixel is as shown in FIG. In the figure, R _LC and C _LC are the equivalent resistance and capacitance of the liquid crystal, and C _DC is the DC blocking capacitance existing at the interface between the switching element M and the liquid crystal. In this circuit,
The waveform of the voltage V _LC applied to the opposite end of the liquid crystal is as shown in FIG. Here, when the sample signal is sampled and held in the capacitor C _LC at the time of each Tji in one frame with respect to the video signal S _V such as A, the level of this signal is B due to leakage through the resistor R _LC. As a result, the effective signal level also decreases.

Therefore, the video signal input considering this level drop
It is necessary to increase the level of S _V , which increases the load on the input circuit described above and also increases the breakdown voltage of the switching element. Furthermore, flicker has occurred due to this level reduction.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention to make it possible to perform signal display with good image quality without flicker with a simple configuration.

SUMMARY OF THE INVENTION According to the present invention, in a liquid crystal display device in which a video signal is sequentially supplied to liquid crystal cells arranged in a matrix to display an image, two sets of the above matrix are alternately arranged in row lines or column lines. Are arranged in combination so that the supplied video signal is switched to a predetermined DC voltage for each field at one timing and the first signal is switched for each field at the opposite timing. A liquid crystal display device in which a direct current potential and a switched second signal are formed, and these two signals are respectively supplied to the two sets of matrices and the two sets of matrices are driven by the same drive signal. Therefore, according to this, it is possible to display an excellent image without flicker with a simple configuration.

Example In FIG. 8, a matrix circuit (shown by adding a dash to the reference numeral) equivalent to the switching elements M _{1 to} Mm, M _{11 to} M _nm and the liquid crystal cells C _{11 to} C _nm is provided, and as shown in the figure. The row lines are arranged alternately in the vertical direction. The control terminals of the switching elements M ₁ ′ to M _m ′ and M ₁₁ ′ to M _nm ′ are connected to the shift registers (2) and (4) in common with each other. Further switching element M ₁ ~Mm, signal input terminal of M ₁ '~M _m' are connected in common, respectively.

Further, the input terminal (1) is connected to one fixed contact of the switch (5) and the other fixed contact of the switch (6). A direct-current voltage source (7) having a predetermined voltage V _DC is connected to the other fixed contact of the switch (5) and one of the switches (6). The switches (5) and (6) are simultaneously switched to one and the other fixed contacts by the field pulse Pf. And this switch (5), is supplied to the signal input terminals of the respective signals from (6) the switching element M ₁ ~Mm and M ₁ '~M _m'.

In this device, the video signal S _V is directly supplied to the input terminal (1) as shown in FIG. 9A. Then, by switching the switches (5) and (6), the switching elements M _{1 to} Mm and M ₁ ′ to M _m ′ are respectively shown in FIGS. 9B and 9C.
As shown in, a signal is supplied in which the video signal and the DC potential alternately appear in each field by opposite tamming. This signal is sampled and held at time Tji, for example, so that the output side of the switching element M in the equivalent circuit of FIG. 6 has an alternating voltage of the signal voltage V _S and the DC voltage V _DC as shown in FIG. 9D. V _LC ′ appears. This voltage V _LC ′ is cut off by the capacitance C _DC , so that a voltage V _LC that changes around the target potential V _T of the terminal (3) is centered on the opposite end of the liquid crystal as shown in FIG. 9E. Is applied.

Therefore, the effective voltage V applied to the opposite end of the liquid crystal
_LCrms is Therefore, even if the input video signal is applied field by field as signal → DC → signal → DC, the information is converted into image information.

The image is displayed in this manner. And in this case,
Since the input video signal has only one polarity, the configuration of the input circuit is simplified. Although the amplitude is required to be doubled, the level is the same, and it is not necessary to increase the load on the circuit and the breakdown voltage of the switching element. Further, since the signal has only one polarity, modulation due to the Early effect or the like does not occur, so that flicker does not occur. Further, the voltage applied to the opposite end of the liquid crystal changes around the target potential and is sampled for each field, so that the occurrence of flicker due to leakage is also reduced.

Furthermore, FIG. 10 shows another example. In this example, switching elements M ₁ ′ to M _m ′, M ₁₁ ′ to M _nm ′ and liquid crystal cell C ₁₁ ′ to
C _nm ′ are arranged horizontally in combination for each column line. Further, the input terminal (1) is provided with a delay circuit (8) for one pixel, and liquid crystal cells C ₁₁ ′ to C ₁₁ are provided on the left side by a switch (9) controlled by a field pulse Pf.
_The signal is delayed only during the period when the video signal is supplied to _nm '. In addition, (10) is a video signal amplifier, and normal amplification is performed. Others are the same as in FIG.

Also in this circuit, the liquid crystal cells C _{11 to} C _nm and C ₁₁ ′ to
A video signal and a DC potential are alternately applied to C _nm 'for each field at opposite timings. Further, the video signal applied to the liquid crystal cells C ₁₁ ′ to C _nm ′ on the left side is delayed by one pixel to align the horizontal position of the display image.

Note that the specific configuration of the input terminal (1) to the amplifier (10) is
As shown in Fig. 11. In the figure, (11) is a clamp circuit. In this circuit, the amplifier (10) does not perform AC drive, so that the configuration is simple.

The delay for one pixel can also be performed by, for example, a sample hold circuit. In that case, sampling can be performed with the clock signal Φ _1H as shown in FIG. 12, for example. Note that FIG. 13 shows a specific configuration example for that purpose.

Further, as shown in FIG. 14, three sample hold circuits (8a), (8b), (8c) are provided, and the circuit (8a) performs sampling with the clock signal Φ _1H , and the circuit (8b),
The sampling may be performed with the clock signal Φ _2H in (8c).

FIG. 15 shows still another example. In this example, four sets of matrix circuits of switching elements M _{1 to} Mm, M _{11 to} M _nm and liquid crystal cells C _{11 to} C _nm (suffixes a, b, respectively) are provided. c, d
Are provided) and are alternately arranged in both horizontal and vertical directions. The signal from the input terminal (1) is supplied to one of the switches (5a) and the other of (5b), and the signal from the delay circuit (8) is supplied to one of the switches (5c) and the other of (5d). , Switches (5a), (5c)
On the other hand, the DC potential is supplied to one of (5b) and (5d), and the signals from the respective switches (5a) to (5d) are supplied to the matrix circuit of the same suffix.

Also in this circuit, a video signal and a DC potential are alternately applied to each liquid crystal cell for each field at a predetermined timing, and horizontal alignment is also performed.

Also in this example, the delay circuit (8) is shown in FIGS.
A sample hold circuit equivalent to that shown in the figure may be used.

Furthermore, in each of the above-described examples, the switching element M can be composed of a MOSFET using a silicon substrate. Alternatively, it may be formed by stacking a thin film transistor and a liquid crystal using amorphous silicon, polysilicon, silicon on sapphire, or the like. In this case, deterioration due to leakage is particularly severe, which is effective.

EFFECTS OF THE INVENTION According to the present invention, it is possible to display an excellent image without flicker with a simple configuration.

[Brief description of drawings]

1 to 7 are views for explaining a conventional apparatus, FIG. 8 is a configuration diagram of an example of the present invention, FIG. 9 is a diagram for the description thereof, and FIG. 10 is a configuration of another example. FIG. 11, FIG. 11 to FIG. 14 are diagrams for explaining the same, and FIG. 15 is a configuration diagram of still another example. (1) is an input terminal, (2) is a shift register, (5),
(6) is a switch, (7) is a DC voltage source, M is a switching element, and C is a liquid crystal cell.

Claims (1)

[Claims] 1. A liquid crystal display device comprising a matrix composed of a plurality of row lines arranged in the vertical direction and a plurality of column lines arranged in the horizontal direction, and having a switching element and a liquid crystal cell arranged at each intersection of the matrix. The switching element and the liquid crystal cell are composed of a first group consisting of the odd-numbered switching element and liquid crystal cell in the vertical or horizontal direction, and an even-numbered switching element and liquid crystal cell adjacent to the first group. A second group, a first signal obtained by switching a video signal and a predetermined DC potential at one timing, and the video signal and the predetermined DC potential at the same timing as the first signal. Is switched so as to be opposite to the first signal, and the switching element and the liquid of the first group and the second group, respectively. In the period in which the predetermined DC potential is supplied to the liquid crystal cell, the liquid crystal cell is supplied with a voltage of about the effective value of the video signal level with respect to the target potential, A liquid crystal display device, wherein the predetermined DC potential is set so that a DC voltage having a polarity opposite to that of the video signal is applied.